299 research outputs found
Non-universal equilibrium crystal shape results from sticky steps
The anisotropic surface free energy, Andreev surface free energy, and
equilibrium crystal shape (ECS) z=z(x,y) are calculated numerically using a
transfer matrix approach with the density matrix renormalization group (DMRG)
method. The adopted surface model is a restricted solid-on-solid (RSOS) model
with "sticky" steps, i.e., steps with a point-contact type attraction between
them (p-RSOS model). By analyzing the results, we obtain a first-order shape
transition on the ECS profile around the (111) facet; and on the curved surface
near the (001) facet edge, we obtain shape exponents having values different
from those of the universal Gruber-Mullins-Pokrovsky-Talapov (GMPT) class. In
order to elucidate the origin of the non-universal shape exponents, we
calculate the slope dependence of the mean step height of "step droplets"
(bound states of steps) using the Monte Carlo method, where p=(dz/dx,
dz/dy)$, and represents the thermal averag |p| dependence of , we
derive a |p|-expanded expression for the non-universal surface free energy
f_{eff}(p), which contains quadratic terms with respect to |p|. The first-order
shape transition and the non-universal shape exponents obtained by the DMRG
calculations are reproduced thermodynamically from the non-universal surface
free energy f_{eff}(p).Comment: 31 pages, 21 figure
'Heat from Above' Heat Capacity Measurements in Liquid He-4
We have made heat capacity measurements of superfluid He-4 at temperatures very close to the lambda point, T(sub lambda) , in a constant heat flux, Q, when the helium sample is heated from above. In this configuration the helium enters a self-organized (SOC) heat transport state at a temperature T(sub SOC)(Q), which for Q greater than or = 100 nW/sq cm lies below T(sub lambda). At low Q we observe little or no deviation from the bulk Q = 0 heat capacity up to T(sub SOC)(Q); beyond this temperature the heat capacity appears to be sharply depressed, deviating dramatically from its bulk behaviour. This marks the formation and propagation of a SOC/superfluid two phase state, which we confirm with a simple model. The excellent agreement between data and model serves as an independent confirmation of the existence of the SOC state. As Q is increased (up to 6 micron W/sq cm) we observe a Q dependant depression in the heat capacity that occurs just below T(sub SOC)(Q), when the entire sample is still superfluid. This is due to the emergence of a large thermal resistance in the sample, which we have measured and used to model the observed heat capacity depression. Our measurements of the superfluid thermal resistivity are a factor of ten larger than previous measurements by Baddar et al
4D Imaging and Diffraction Dynamics of Single-Particle Phase Transition in Heterogeneous Ensembles
In this Letter, we introduce conical-scanning dark-field imaging in four-dimensional (4D) ultrafast electron microscopy to visualize single-particle dynamics of a polycrystalline ensemble undergoing phase transitions. Specifically, the ultrafast metal–insulator phase transition of vanadium dioxide is induced using laser excitation and followed by taking electron-pulsed, time-resolved images and diffraction patterns. The single-particle selectivity is achieved by identifying the origin of all constituent Bragg spots on Debye–Scherrer rings from the ensemble. Orientation mapping and dynamic scattering simulation of the electron diffraction patterns in the monoclinic and tetragonal phase during the transition confirm the observed behavior of Bragg spots change with time. We found that the threshold temperature for phase recovery increases with increasing particle sizes and we quantified the observation through a theoretical model developed for single-particle phase transitions. The reported methodology of conical scanning, orientation mapping in 4D imaging promises to be powerful for heterogeneous ensemble, as it enables imaging and diffraction at a given time with a full archive of structural information for each particle, for example, size, morphology, and orientation while minimizing radiation damage to the specimen
Measurements of and production in proton–proton interactions at in the NA61/SHINE experiment
Double-differential yields of and
resonances produced in \pp interactions
were measured at a laboratory beam momentum of 158~\GeVc. This measurement is
the first of its kind in \pp interactions below LHC energies. It was performed
at the CERN SPS by the \NASixtyOne collaboration. Double-differential
distributions in rapidity and transverse momentum were obtained from a sample
of 2610 inelastic events. The spectra are extrapolated to full phase
space resulting in mean multiplicity of (6.73
0.25 0.67) and (2.71
0.18 0.18). The rapidity and transverse momentum
spectra and mean multiplicities were compared to predictions of string-hadronic
and statistical model calculations
Erratum to: Measurements of , , p and spectra in Be+Be collisions at beam momenta from 19A to 150A GeV/c with the NA61/SHINE spectrometer at the CERN SPS – NA61/SHINE Collaboration
Measurements of and production in proton–proton interactions at in the NA61/SHINE experiment
International audienceThe production of and hyperons in inelastic p+p interactions is studied in a fixed target experiment at a beam momentum of 158 . Double differential distributions in rapidity and transverse momentum are obtained from a sample of 33M inelastic events. They allow to extrapolate the spectra to full phase space and to determine the mean multiplicity of both and . The rapidity and transverse momentum spectra are compared to transport model predictions. The mean multiplicity in inelastic p+p interactions at 158 is used to quantify the strangeness enhancement in A+A collisions at the same centre-of-mass energy per nucleon pair
Two-particle correlations in azimuthal angle and pseudorapidity in central collisions at the CERN Super Proton Synchrotron
Measurements of , , p and spectra in Be+Be collisions at beam momenta from 19A to 150A with the NA61/SHINE spectrometer at the CERN SPS
The NA61/SHINE experiment at the CERN Super Proton Synchrotron (SPS) studies the onset of deconfinement in hadron matter by a scan of particle production in collisions of nuclei with various sizes at a set of energies covering the SPS energy range. This paper presents results on inclusive double-differential spectra, transverse momentum and rapidity distributions and mean multiplicities of π ±
π±
, K ±
K±
, p and p ¯
p¯
produced in the 20% most central 7
7
Be+ 9
9
Be collisions at beam momenta of 19A, 30A, 40A, 75A and 150A GeV/c
GeV/c
. The energy dependence of the K ±
K±
/π ±
π±
ratios as well as of inverse slope parameters of the K ±
K±
transverse mass distributions are close to those found in inelastic p+p reactions. The new results are compared to the world data on p+p and Pb+Pb collisions as well as to predictions of the Epos, Urqmd, Ampt, Phsd and Smash models
Measurements of , , p and spectra in Be+Be collisions at beam momenta from 19A to 150A with the NA61/SHINE spectrometer at the CERN SPS
The NA61/SHINE experiment at the CERN Super Proton Synchrotron (SPS) studies the onset of deconfinement in hadron matter by a scan of particle production in collisions of nuclei with various sizes at a set of energies covering the SPS energy range. This paper presents results on inclusive double-differential spectra, transverse momentum and rapidity distributions and mean multiplicities of π ±
π±
, K ±
K±
, p and p ¯
p¯
produced in the 20% most central 7
7
Be+ 9
9
Be collisions at beam momenta of 19A, 30A, 40A, 75A and 150A GeV/c
GeV/c
. The energy dependence of the K ±
K±
/π ±
π±
ratios as well as of inverse slope parameters of the K ±
K±
transverse mass distributions are close to those found in inelastic p+p reactions. The new results are compared to the world data on p+p and Pb+Pb collisions as well as to predictions of the Epos, Urqmd, Ampt, Phsd and Smash models
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